1. Field of the Invention
The present invention relates to a digital information recording carrier having digital information recorded in the form of a two-dimensional pattern on a recording surface of the carrier. The invention also relates to a digital information recording method and apparatus which can produce such digital information carriers. Further, the invention relates to a digital information decoding method and apparatus which can read and decode digital information recorded on such a digital information carrier.
2. Description of the Prior Art
FIG. 50 shows a two-dimensional data code which has been used in a method for recording digital information by arraying a matrix two-dimensionally on a recording surface (see U.S. Pat. No. 4,939,354). The two-dimensional data code is to record digital information by virtually setting matrix cells corresponding to bits on a recording surface 220 of a recording carrier, and by assigning to each cell a white or black color representing data.
In such a recording method, generally, control information representing the orientation of an information recording area 219 and the size of a cell (data density) is provided for reading convenience""s sake. In the example of FIG. 50, as the control information, the perimeter of the rectangular information recording area 219 is provided with a linear portion 212 on its two adjoining sides 221 and a clocking information portion 216 on the remaining two sides 231. The linear portion 212 is formed of adjoining black cells, and the clocking information portion 216 is formed of alternately connected white and black cells. During a reading operation, the orientation of the information recording area 219 is detected due to the linear portion 212, and the size of cells is detected through the clocking information portion 216.
In the above conventional digital information recording method, however, the clocking information portion 216 will be farther away from the data as the size of the information recording area 219 increases. This is because the clocking information portion 216 is provided along the perimeter of the information recording area 219. As a result, due to factors such as distortion of the recording surface 220, characteristics of the reading device (scanner, CCD camera, etc.), or the like, a large difference in data position between recording and reading operations will be caused in the vicinity of the center of the information recording area 219, resulting in reading errors. For example, instead of originally intended information on a cell of the fifth row, the fourth column, the information on the cell of the sixth row, the fifth column may be erroneously read. Consequently, the conventional digital information recording method has a problem that the size of the information recording area 219 cannot be increased and therefore that the storage capacity cannot be increased.
The present invention has been developed with a view to substantially solving the above described disadvantages and has for its essential object to provide a digital information recording carrier which can prevent the occurrence of reading errors over the entire range of the information recording area even if the size of the information recording area is increased, and therefore which allows the storage capacity to be increased.
Another object of the present invention is to provide a digital information recording method and apparatus which can produce such a digital information recording carrier.
A still further object of the present invention is to provide a digital information decoding method and apparatus which can read and decode digital information recorded on such a digital information recording carrier.
In order to achieve the aforementioned objects, the present invention provides a digital information recording carrier, comprising:
a planar recording surface having an information recording area in which cells corresponding to bits are virtually set in a matrix form, each cell being provided with an optically recognizable mark corresponding to digital information so that the digital information is recorded in the information recording area as a two-dimensional pattern; and
specific patterns each consisting of a plurality of cells which are linked together or contiguous and which are given optically recognizable marks in a given pattern, the specific patterns including a predetermined pattern which is placed in an inner portion apart from a perimeter of the information recording area.
In this digital information recording carrier, predetermined patterns are disposed inside, spaced from the perimeter of the information recording area. Therefore, even if the information recording area is distorted in the vicinities of its center, the positions of cells in the vicinities of the center of the information recording area are accurately determined based on the positions of the specific patterns. Accordingly, few or no reading errors will occur in the vicinities of the center of the information recording area even if the size of the information recording area is increased. Also, for the peripheral part of the information recording area, the occurrence of reading errors is prevented by providing clocking information as in the prior art or by providing the specific patterns. As a consequence, it is possible to increase the storage capacity by increasing the size of the information recording area.
In one embodiment, the specific patterns are dispersedly arranged all over the information recording area. In this case, the position of any arbitrary cell is accurately determined over the entire range of the information recording area. As a consequence, it is possible to increase the storage capacity by increasing the size of the information recording area.
In one embodiment, the cells each have a shape of a square of same size. And, each specific pattern is composed of a central closed area with a shape of a square and a loop portion surrounding the central closed area entirely. The central closed area consists of four cells each provided with a light as an optically recognizable mark and the loop portion consists of twelve cells each provided with a dark as an optically recognizable mark.
In another embodiment, each specific pattern is composed of a central portion with a shape of a square, a first loop portion surrounding the central portion entirely, and a second loop portion surrounding the first loop portion entirely. The central portion consists of a single cell provided with a dark as an optically recognizable mark, the first loop portion consists of eight cells each provided with a light as an optically recognizable mark, and the second loop portion consists of sixteen cells each provided with a dark as an optically recognizable mark.
In these cases, it is easy to find the specific patterns in the information recording area. Also, the number of cells constituting the specific pattern is relatively small. Further, when an identical or similar pattern appears nearby as the recorded information, the specific pattern will not easily overlap the nearby pattern. Still, the specific pattern is less affected by dirt or ink blurs during printing. Besides, the algorithm to find the specific patterns becomes simplified.
In one embodiment, the specific patterns are arranged with higher density in a peripheral part of the information recording area than in an interior of the information recording area. In this case, the reading precision for the peripheral part where distortion is more likely to occur due to the reading device characteristics is enhanced so that the occurrence of reading errors is prevented.
In another embodiment, the specific patterns are placed with higher density in the interior of the information recording area than in the peripheral part of the information recording area. In this case, the reading precision for the vicinities of the center of the information recording area is enhanced so that the occurrence of reading errors is prevented.
In one embodiment, the information recording area is a rectangular area having four corners and a specific pattern is placed at each corner. In this case, searching for the specific patterns placed at the four corners allows an easy determination of the range occupied by the information recording area within the recording surface.
In one embodiment, the specific patterns placed at the four corners are different from the specific patterns placed in the other portions of the information recording area. In this case, searching for the specific patterns different from the others allows a still easier determination of the range occupied by the information recording area within the recording surface.
In one embodiment, part of the specific patterns placed at the four corners are different from the rest thereof such that a set of the specific patterns placed at the four corners becomes asymmetrical with respect to a 90xc2x0, 180xc2x0, or 270xc2x0 rotation on the recording surface. This arrangement makes it easy to recognize top and bottom or right and left of the information recording area.
In one embodiment, the specific patterns have a light and a dark as the optically recognizable marks, and a light/dark status of some of the specific patterns is inverse to that of the other specific patterns so as to make a contrast against nearby cells in which digital information has been recorded. In this case, it is easy to recognize boundaries between the specific patterns and the surrounding information-recorded cells. This allows an easy search for the specific patterns.
The present invention further provides a digital information recording method, comprising the steps of:
virtually setting cells corresponding to bits in a matrix form in an information recording area provided within a planar recording surface;
placing specific patterns at least in an interior of the information recording area apart from a perimeter of the information recording area, wherein each specific pattern consists of a plurality of cells which are linked together and which are given optically recognizable marks in a given pattern; and
providing each of the cells present in regions other than regions occupied by the specific patterns of the information recording area with an optically recognizable mark corresponding to digital information to be recorded so that the digital information is recorded in the information recording area as a two-dimensional pattern.
This digital information recording method can easily produce the digital information recording carriers according to the above-described various embodiments of various types.
In one embodiment, the digital information recording method further comprises the steps of:
comparing light/dark statuses of cells defining a perimeter of each specific pattern with light/dark statuses of information-recorded cells which are immediately adjacent to the perimeter of the specific pattern; and
inverting, if the compared light/dark statuses are coincident with each other, the light/dark statuses of constituent cells of the specific pattern such that the specific pattern is distinguished from the adjacent information-recorded cells.
In this case, it is easy to recognize the boundaries between the specific patterns and the information-recorded cells immediately adjacent to the specific patterns on the recording surface of the generated digital information recording carrier. This allows an easy search for the specific patterns.
The present invention also provides a digital information recording apparatus which comprises the steps of:
searching the information recording area for the specific patterns to determine their positions;
calculating positions of arbitrary information-recorded cells by a proportional allocation technique, based on positions of four specific patterns out of all the searched specific patterns, the four specific patterns being placed on two given rows and two given columns;
reading bit information of each cell located at the calculated position; and
reproducing the digital information recorded on the recording surface based on the read bit information.
In order to decode the digital information recorded on the digital information recording carrier wherein the cells each have a shape of a square of same size, wherein each specific pattern is composed of a central closed area with a shape of a square and a loop portion surrounding the central closed area entirely, and wherein the central closed area consists of four cells each provided with a light as an optically recognizable mark and the loop portion consists of twelve cells each provided with a dark as an optically recognizable mark,
the step of searching the information recording area for the specific patterns comprises the sub-steps of:
checking the light/dark status of a reference position for a search for the central closed area of the specific pattern, to decide that the reference position is contained in the central closed area if the light/dark status of the reference position is a light; and
checking a region occupied by lights which are linked to each other, the reference position being included in the region, as to whether or not size, width, and height of the region are within certain ranges, respectively, to confirm that the region is the central closed area.
Further, in order to decode the digital information recorded on the digital information recording carrier wherein each specific pattern is composed of a central portion with a shape of a square, a first loop portion surrounding the central portion entirely, and a second loop portion surrounding the first loop portion entirely, and wherein the central portion consists of a single cell provided with a dark as a mark, the first loop portion consists of eight cells each provided with a light as a mark, and the second loop portion consists of sixteen cells each provided with a dark as a mark,
the step of searching the information recording area for the specific patterns comprises the sub-steps of:
checking the light/dark status of a reference position for a search for the central closed area of the specific pattern, to decide that the reference position is contained in the central closed area if the light/dark status of the reference position is a dark;
checking a first dark region occupied by darks which are linked to each other, the reference position being included in the first dark region, as to whether or not size, width, and height of the first dark region are within certain ranges, respectively, to confirm that the first dark region is the central closed area; and
confirming, when a second dark region appears within a certain distance upward, downward, rightward or leftward from the first dark region after a light region has appeared and when a loop has been made around a boundary between the light region and the second dark region, that the light region is the first loop portion.
The present invention further provides a digital information recording apparatus for recording digital information as a two-dimensional pattern in an information recording area provided within a planar recording surface, wherein cells corresponding to bits are virtually set in a matrix form in the information recording area and the recording of digital information is executed by providing an optically recognizable mark corresponding to the digital information to each of the cells. In the digital information recording apparatus, input means take in digital information to be recorded into the digital information recording apparatus. Then, pattern generating means generate a two-dimensional pattern to be printed onto the recording surface, by placing specific patterns inside of the information recording area apart from its perimeter, the specific patterns being each formed of a plurality of linked cells provided with optically recognizable marks in a given pattern, and by placing the digital information in regions of the information recording area other than regions occupied by the specific patterns. Finally, printing means print the two-dimensional pattern generated by the pattern generating means onto the recording surface. Using this digital information recording apparatus allows an easy generation of the aforementioned various types of digital information recording carriers.
Further, the present invention provides a digital information decoding apparatus for reading and decoding digital information from the aforementioned various types of digital information recording carriers. In the digital information decoding apparatus, reading means read the two-dimensional pattern recorded on the recording surface and output information representing the two-dimensional pattern. Then, information decoding means reproduce the digital information recorded on the recording surface in the following way. The information decoding means first search inside of the two-dimensional pattern represented by the output information of the reading means for the specific patterns to determine positions thereof, then calculate positions of arbitrary information-recorded cells by a proportional allocation technique based on the positions of four specific patterns out of all the searched specific patterns, the four specific patterns being placed on two given rows and two given columns, then read bit information of each cell located at the calculated position, and then reproduce the digital information recorded on the recording surface based on the read bit information. Finally, output means output the digital information reproduced by the information decoding means. Using this apparatus allows an easy decoding of digital information recorded on the digital information recording carrier.